Hi veenu08,

The technical explanation for answers A vs. E might come across as long-winded, so I'll do my best to keep it simple.

In answer A, the word "who" is a pronoun that represents the subject "Robinson." In this sentence, it comes across as redundant since we already know that Robinson is the subject. It would be the same as writing "Robinson is a Botanist and he has a dream...."; the sentence doesn't require a pronoun to be correct, so the pronoun probably shouldn't be there.

In answer E, the word "whose" is a possessive pronoun that links "dream" to "Robinson" (so we know it's Robinson's dream, without having to write "and he has a dream"). From a "style" standpoint, it's preferable to eliminate redundancies and this answer does so.

GMAT assassins aren't born, they're made,
Rich